1. Field of the Invention
This invention relates to silicone rubber molding compositions and a method for producing silicone rubber molded parts therefrom using a mold.
2. Background Art
Silicone rubber is used in a variety of applications because of heat resistance, low-temperature resistance and electrical properties. A variety of methods are known for molding silicone rubber compounds. Depending on a particular application or purpose, a choice is made from among compression molding, transfer molding, injection molding and extrusion molding (or hot air vulcanization).
These molding methods, however, suffer from the problem of inefficient operation. That is, when silicone rubber compounds are molded into silicone rubber parts using molds, the molded silicone rubber cannot be smoothly released from the mold.
Known solutions to this problem include the chromium plating of a mold surface and the coating of a mold surface with fluorocarbon resin. The chromium plating is still insufficient in parting properties. The coating of fluorocarbon resin is expensive. It is also known to apply abherents such as surfactants, halocarbon polymers and talc to molds. The coatings of such abherents are not sustainable and can contaminate molded parts.
In order to improve the release properties of silicone rubber itself, JP-B 45099/1980 and U.S. Pat. No. 3,549,744 propose to blend carboxylic acids or metal salts thereof in silicone rubber compositions. These additives largely detract from the compression set and flame retardancy of silicone rubber and impart insufficient release properties.
JP-B 19951/1980 discloses blending of metal salts of higher fatty acids, JP-A 44655/1982 discloses blending of high fatty acids, and JP-A 194949/1983 discloses a mixture of an amide and polytetrafluoroethylene (PTFE). These additives detract from heat resistance and impart insufficient release properties.